1. Field of the Invention
The present invention relates generally to aviation sensor and display technology, and particularly to dual-axis loadmeter systems for ground based training and for airborne systems.
2. Technical Background
At some point in time in the history of aviation, aircraft structural design parameters were defined using a two-dimensional plot of acceleration versus velocity. This two-dimensional curve was commonly referred to as the “flight envelope.” While materials, designs, and design parameters have changed and improved over the years, the term flight envelope is still understood as a term that refers to the load factor limits of a particular aircraft design. All structures, of course, have failure modes. When enough force is applied to an object, the object will ultimately deform and fail. This applies to aircraft components/systems such as airframes, engine components, connective elements, wings, rudders, and etc.
Accordingly, each aircraft type is defined by a unique set of limit loads corresponding to the flight envelope. If a load is applied to the aircraft in excess of a predetermined value, i.e., the ultimate limit load, one can expect the aircraft to experience a mechanical failure. The limit load is typically a function of the mechanical properties of the materials comprising the component structures, and therefore, different types of aircraft perform differently, with some being more robust than others. In practice, designers often specify a given aircraft's “limit load” as some arbitrary number lower than the ultimate load. The difference between the limit load and the ultimate limit load, therefore, represents a safety factor. Often, the limit load is selected by dividing the ultimate load by a factor of 1.5 to thereby provide a 50% safety factor.
Thus, an aircraft is being operated safely if a given maneuver is within the flight envelope, i.e., the forces applied to the aircraft during the maneuver should not cause a failure to occur. An “envelope condition” refers to a scenario wherein the aircraft is being operated outside the “envelope”—the pilot attempts a maneuver that results in the application of forces that result in a structural failure. For example, in recent memory, a fatal accident occurred when a pilot improperly operated the pedal controls of the aircraft to effect a rudder hardover event. Excessive forces were applied to the rudder and eventually the tail section separated from the aircraft. Obviously, the pilot had no intention of causing the aforementioned failure mode. The accident occurred because the pilot did not have an a priori understanding of the causal link between his actions and the failure mode.
The ability to safely operate an aircraft is a learned skill. In general, the more experienced a pilot is, the less apt he or she is to maneuver the aircraft in an unsafe manner outside the flight envelope. Thus, it is imperative that a trainee master certain skills before assuming the controls of an aircraft. Accordingly, initial flight training is often provided using a ground-based aircraft surrogate training device—i.e., a ground-based flight simulator. A flight simulator provides a trainee with a safe and cost effective flight training environment. Flight simulators enhance safety because they allow the students to make potentially fatal mistakes, such as operating the aircraft outside the flight envelope, without bearing the unfortunate consequences.
Ground-based flight simulators are also used by experienced pilots as well. Flight simulators may be used to provide experienced pilots with valuable training time for maintaining their skill level. Simulators are cost effective because the cost of fuel, landing fees, and aircraft maintenance costs are avoided. Furthermore, such simulators may be employed to teach an experienced pilot new procedures. They also may be used to teach an experienced pilot how to fly a new, or different, type of aircraft than he or she is used to flying.
Conventional ground-based aircraft simulators may be implemented in a variety of training systems including desk-top trainers, part task trainers or full-flight simulators. One drawback to all of these systems methods relates to their inability to generate the “real-world” accelerations—“g-forces” or “g's”—that pilots experience when an identical maneuver is performed on board an aircraft in flight. The ability of the human body to sense g-forces is an important, and indeed an invaluable, feedback mechanism that provides the pilot with a biological signal indicating whether or not a maneuver is being performed correctly. Certain large amplitude training maneuvers generate significant accelerations, and if performed incorrectly, may drive the aircraft into an envelope condition.
Acceleration is measured on board the aircraft with a device commonly referred to as a G-meter. A G-meter may also be referred to as a loadmeter. In its simplest form, a g-force sensor may be implemented using a spring supported mass mechanically coupled to a potentiometer. Of course, the mass is “calibrated” such that it moves in a predetermined manner in response to a corresponding g-force. The movement of the mass changes the resistance of the potentiometer to thereby provide an analog voltage signal as a function of the g-force. Of course, any suitable sensor may be employed. More sophisticated acceleration sensors may use MEMS based accelerometers. In any event, the G-meter is implemented by coupling the sensor to a display mechanism. Some conventional G-meters are realized using a dial having a single needle. Other conventional implementations provide this information in a digital format via an LCD display, for example. In either case, the display is an indication of the g-force measurement at the aircraft centroid or at a point along the centerline of the aircraft.
Unfortunately, the conventional G-meters briefly described above have drawbacks. For example, conventional devices do not provide any measurement of differential g-forces caused by aircraft roll maneuvers or by other such asymmetric loading conditions. Conventional G-meters do not measure or display lateral g's caused by rudder loads. What is needed, therefore, is a loadmeter that is configured to display vertical g-forces, differential g-forces applied along the wingspan, lateral accelerations, and rudder loads relative to the predetermined load limits of the aircraft in real time.
What is also needed is a ground-based aircraft surrogate training device configured to provide a trainee with real-time information corresponding to the g-forces generated by a particular maneuver on a particular type of aircraft. The lack of such information is detrimental to flight training because the trainee may complete a potentially dangerous maneuver in a simulator without becoming unaware of the effects of that particular maneuver on the aircraft. The trainee walks away from the training experience with an inaccurate perception of the effects of the attempted maneuver. The consequences of the trainee's ignorance could be disastrous if an identical maneuver is attempted in flight.
Thus, a loadmeter configured to display vertical g-forces, differential g-forces applied along the wingspan, lateral accelerations, and rudder loads in real time relative to the predetermined load limits of the aircraft is needed for both ground-based simulator applications as well as airborne applications.